The present invention relates to an optical pick-up used for recording information to and/or reproducing information from three types of optical discs of different standards including CD, DVD and a high recording density optical disc (e.g., HD DVD or BD).
An optical pick-up configured to use a common objective lens for all of a plurality of types of optical discs of different standards has become widespread. Japanese Patent Provisional Publication No. HEI 9-306024 (hereafter, referred to as JP HEI 9-306024A) discloses an optical pick-up employing a common objective lens used for CD and DVD. The optical pick-up disclosed in JP HEI 9-306024A is configured to change magnification of the objective lens in accordance with the type of the optical disc being used to suppress aberrations caused by temperature variations. More specifically, in the optical pick-up, a converging light beam is incident on the objective lens when DVD is used, while a substantially collimated beam is incident on the objective lens when the CD is used.
Japanese Patent Provisional Publication No. 2004-247025 (hereafter, referred to as JP 2004-247025A) discloses an optical information recording/reproducing device for recording information to and/or reproducing information from a plurality of types of optical discs, such as CD, DVD and an optical disc which achieves a recording density higher than that of DVD through use of blue laser. In JP 2004-247025A, two types of optical systems are disclosed. A first optical system (disclosed in the 1st and 2nd embodiments in JP 2004-247025A) forms an infinite optical system for each of the plurality of types of optical discs. That is, in the first optical system, a collimated beam is incident on an objective lens for each of the plurality of types of optical discs. A second optical system (disclosed in the 3rd embodiment in JP 2004-247025A) forms a finite optical system for each of the plurality of types of optical discs. In the second optical system a diverging beam is incident on the objective lens for each of the plurality of types of the objective lenses.
In each of the first and second optical systems, the objective lens is provided with a diffraction structure designed to achieve the desired diffraction efficiency through use of different orders of diffraction light for light beams having different wavelengths while securing the desired light amount. Regarding the infinite optical system, an optical element having an optical correction structure for temperature compensation or chromatic aberration compensation is placed on an optical path. Regarding the finite optical system, a diffraction structure is formed on a coupling lens in addition to forming a diffraction structure on the objective lens because the tracking performance of the finite optical system is inferior to that of the infinite optical system and the temperature characteristic of the finite optical system may deteriorate particularly when a diverging beam is incident on the objective lens.